The effects of imperfections on the performance of the subharmonic vibration absorber system

A recent study has demonstrated a new configuration of centrifugal pendulum vibration absorbers (CPVAs) that is very effective at reducing torsional vibration levels in rotating systems that are subjected to harmonic external torques. This system is composed of a pair of absorber masses riding on epicycloidal paths that are tuned to one-half order relative to the frequency of the applied torque. In the desired response, the two absorbers move in direct opposition to one another in a second-order subharmonic manner. The basic analysis of this subharmonic vibration absorber system assumes that the paths for the absorber masses can be perfectly manufactured and are exactly tuned as desired. The primary goal of this study is to explore the effects that imperfections and intentional mistuning of the absorber paths have on performance of the system. The results obtained allow one to select certain features of the path in order to achieve the desired performance, even in the face of uncertainties. To this aim, the equations of motion are first derived for a simplified model, consisting of two absorber masses and a rigid rotor. This system is shown to possess a one-to-one internal resonance subjected to two-to-one resonant external excitation. By making use of some scaling assumptions on the system parameters, the method of averaging is applied in order to obtain approximate solutions of the equations of motion. These are used to evaluate the absorber performance in terms of two performance measures: the magnitude of the rotor acceleration and the range of the disturbing torque over which the absorbers operate effectively. The results obtained are distilled into design guidelines in terms of how one should choose certain mistuning parameters for the absorber paths in order to achieve satisfactory system performance. In summary, it is determined that one should keep the two absorber paths as identical as possible, but that a small level of identical overtuning in each path will provide a certain level of robustness. In addition, it is also shown that this mistuning can be used to adjust a tradeoff between torsional vibration levels and the operating torque range for the system. (C) 1998 Academic Press.